Study of Inhomogeneous Residual Stress Fields by Drilling a “Large Hole” in Combination with Phase Shifting Shearing Interferometry

A technique for recording tangential displacements in the zone of a hole-indicator of residual stresses by electronic digital speckle interferometry using phase-shifting interferometry is developed, which provides for the possibility of effective practical application of “large hole” drilling for studying nonuniform fields of residual stresses in flat parts. A circuit of an interferometer for electronic digital speckle interferometry is proposed, in which a step-by-step (up to 20 steps) phase shift of the object beam is set using a special unit—a phase modulator. This allows recording many interferograms that are different from each other in the form of intensity patterns with known phase shift values, providing for the possibility of obtaining highly accurate information on displacement fields in a wide range of displacements. Using the “large hole” drilling method, residual stresses in the weld butt seam zone and the weld-affected zone of a steel sample have been studied. The results of such study for four cases of successively increasing hole diameters showed that the developed technique ensures high accuracy of results in studies of nonuniform high-gradient distributions of residual stresses.